The American Academy of Ophthalmology has reported that about two million people in the United States have primary open angle glaucoma (the most common of several types of glaucoma). About seven million office visits are made each year by people with glaucoma or those suspected of having glaucoma. Glaucoma is the second leading cause of legal blindness in the United States and the leading cause of legal blindness in African-Americans. About 80,000 people in the United States alone are legally blind from glaucoma, not counting those with lesser visual impairment.
By definition, glaucoma is a group of eye diseases characterized by an increase in intraocular pressure which causes pathological changes in the optic disc and nerve fiber layer of the retina with resultant typical defects in the field of vision. The relationship between glaucoma and intraocular pressure is fundamental to proper treatment planning for glaucoma.
Normal intraocular pressure is considered to be less than 22 mm Hg. However, at least one in six patients with glaucoma may have pressure below this normal level and yet still have progressive eye damage. Also, at any single test, about one half of all glaucoma patients will exhibit measured intraocular pressures below 22 mm Hg but actually will have average intraocular pressures higher than 22 mm Hg. This makes frequent testing necessary to obtain an accurate assessment of a patient's average intraocular pressure.
Most current methods of routine intraocular pressure measurements rely on applanating a plunger against the cornea. The degree to which a portion of the cornea is deformed indicates the pressure inside the eye resisting this deformation. All of these methods are inferring the intraocular pressure rather than measuring it directly. Some specialists believe that the thickness of the cornea can vary from person to person, and that other factors such as corneal scars or previous surgery may affect the accuracy of these measurements. Also, most of these methods require that topical anesthesia be placed on the cornea prior to measuring the pressure and the measurements be made by trained personnel. Therefore, there is a need to develop techniques to make repeated and/or continuous measurements and to enable persons other than trained personnel to make such measurements.
U.S. Pat. No. 5,005,577 discloses an intraocular lens pressure monitoring device based on radiosonde technology. Radiosonde technology has been around for decades. The idea of using radiosonde technology for intraocular pressure monitoring was proposed in the '577 patent. However, it is unknown from the '577 patent how to make or use such an intraocular pressure monitoring device to carry out the invention. Specifically, the technology disclosed in the '577 patent has not been miniaturized in such a way to make it possible to insert into the eye.
Further, the '577 patent discloses an intraocular lens pressure monitoring device as a part of an integrated intraocular lens system, not a stand-alone device. If replacement of the monitoring device is needed, it would be difficult to separate the device from the lens without major surgery.
The '577 patent also discloses active sensors. An active sensor usually includes a power supply and a transmitter. As indicated in the '577 patent, an active sensor is generally too large in size to be implanted in the eye. Although it is speculated that technology will progress to the point to allow an active sensor to be implanted in the eye, the patentee does not, in fact, know what technology may be used and how it could be used to resolve the above-mentioned problems and addresses the above-mentioned concerns.
Accordingly, there is a need for a miniaturized device capable of inserting into an eye to monitor/measure intraocular pressure accurately, frequently, and continuously. There is also a need for a stand-alone intraocular pressure monitoring/measuring device separate from an intraocular lens system.